油气田套管用钢两相流流动腐蚀

Flow corrosion of casing steel for oil and gas field in two-phase flow

采用旋转圆柱电极流动腐蚀装置并辅以电化学工作站,研究了不同砂粒质量分数、不同流动腐蚀时间对N80油气井套管钢在含砂、含Cl-液固两相流中流动腐蚀的失重速率和腐蚀电化学行为的影响规律.利用Smartzoom 5超景深三维数码显微镜对流动腐蚀后试样表面进行分析表征.结果表明:N80钢在含砂、含Cl-液固两相流中的流动腐蚀形貌为典型的颗粒切削痕迹,并伴有腐蚀凹坑,流动腐蚀机理为机械冲刷和电化学腐蚀协同作用;在砂粒质量分数1%~3%的范围内,随砂粒质量分数增大,流动腐蚀速率增大,砂粒质量分数增大到4%以上后,较大的砂粒质量分数形成“屏蔽作用”,反而降低了流动腐蚀速率;在2种因素变化情况下,N80钢流动腐蚀阴极极化曲线极化率远大于阳极极化曲线极化率,腐蚀反应受阴极氧的去极化反应控制;随时间的增加,N80钢流动腐蚀失重量呈线性增加,腐蚀速率逐渐降低,在9 h时达到最低,之后腐蚀速率反而升高.

The influence of different silica sand mass fractions and flow corrosion time on the mass loss rate and corrosion electrochemical behavior of N80 casing steel in liquid-solid two-phase flow fluid containing silica sand and chloride ion was investigated with a rotating cylindrical electrode device and an electrochemical workstation.The surface of specimens after flow corrosion was characterized and analyzed by three-dimensional digital microscope Smartzoom 5.The results show that the flow corrosion morphology of N80 steel in liquid-solid two-phase flow containing silica sand and chloride ion is typical particle cutting trace with a few corrosion pits,and the mechanism of flow corrosion is synergistic inte-raction between erosion and corrosion processes.In the range of sand mass fraction from 1%to 3%,the flow corrosion rate increases with the increase of sand mass fraction.However,when the sand mass fraction increases to more than 4%,larger sand content forms a″shielding effect″,which reduces the flow corrosion rate.With the variation of two factors,the polarization rate of the cathode polarization curve is much higher than that of the anode polarization curve for N80 steel flow corrosion process.The corrosion reaction is controlled by oxygen depolarization reaction of cathode.With the increase of time,the mass loss of N80 steel in liquid-solid two-phase flow fluid increases linearly,and the corrosion rate gradually decreases which reaches the lowest at 9 h and then increases.